In the fields of electronics and displays, electronic circuits and active matrices are conventionally manufactured using a photolithography process. Recently, the so-called printed electronics technology is developing for manufacturing such electronic devices using a printing process. Various printing methods such as micro-contact printing, gravure printing, and screen printing are being considered for use in printed electronics. Inkjet printing is one of such printing methods. The inkjet printing method involves discharging ink droplets from a nozzle of an inkjet head and causing the ink droplets to land on a substrate to be printed. An inkjet head typically includes a nozzle plate and a liquid chamber forming plate. The nozzle plate includes a discharge outlet arranged at a nozzle surface and a nozzle hole corresponding to a hollow portion in connection with the discharge outlet that penetrates through the nozzle plate in the thickness direction. The liquid chamber forming plate is bonded with the nozzle plate to form an ink liquid chamber that is in connection with the nozzle hole corresponding to the hollow portion of the nozzle plate. Such an inkjet head is configured to selectively discharge ink droplets from the discharge outlet by using a drive means to apply a force to an ink meniscus formed at the discharge outlet. The drive means may be implemented by a system using electrostatic force, a system using a piezoelectric element, or a system using thermal element, for example.
In the case of using the inkjet printing method in printed electronics, because wiring of an electronic circuit is printed, a high resolution ranging from about a submicron to 10 μm is required. In view of such a requirement, the diameter of the discharge outlet formed on the nozzle plate needs to be less than or equal to 10 μm. Accordingly, various techniques have been proposed relating to the shapes and manufacturing methods of nozzle plates of inkjet heads. For example, Japanese Laid-Open Patent Publication No. 10-034365 (Patent Document 1) discloses a method of manufacturing a nozzle plate that involves irradiating a laser beam on the surface of a substrate that is to become a nozzle plate in its thickness direction. By irradiating the laser beam in the thickness direction of the substrate, portions of the substrate irradiated by the laser beam are melted so that a through hole reaching the rear face of the substrate is formed. In this way, a nozzle plate having a discharge outlet formed at the surface of the substrate and a nozzle hole corresponding to a hollow portion in connection with the discharge outlet that penetrates through the substrate in its thickness direction to reach the rear face of the substrate may be manufactured.
However, in the nozzle plate manufacturing method disclosed in Patent Document 1, a laser beam is continuously irradiated on the surface of the substrate while the nozzle hole corresponding to a through hole reaching the rear face of the substrate is being formed. As a result, the temperature of the substrate near the surface of the substrate becomes higher than that near the rear face of the substrate and a temperature distribution in the thickness direction is created from the surface of the substrate to the rear face of the substrate. This causes an opening area of the discharge outlet at the surface of the substrate to be larger than the opening area of nozzle hole at the rear face of the substrate. Also, in the case of forming nozzle holes by scanning a laser beam, a discharge outlet pitch may be reduced by densifying the nozzle holes. However, when the pitch is reduced, residual heat from forming a preceding discharge outlet may remain when forming a present discharge outlet so that the temperature of an area near the previously formed discharge outlet may be higher than the remaining areas. As a result, the shape of the present discharge outlet may vary from a desired target shape. Thus, wide variations may be created in the opening areas of the discharge outlets and the opening shapes of the discharge outlets may be irregular and unstable as well. Further, in the case of forming a nozzle hole using a laser beam, the opening shape of the discharge outlets is limited to circular shapes or oval shapes. When ink is discharged from a discharge outlet of a nozzle plate having such an opening shape, ink mists or ink satellites may be formed to thereby hinder high quality printing.